The cells of most fungi grow as tubular, elongated and thread like structures called hyphae which may contain multiple nuclei and which extend by growing at their tips. This is in contrast to similar-looking organisms, such as filamentous green algae, which grow by repeated cell division with a chain of cells.
The collective body of hyphae that constitutes the vegetative stage of a fungus is called a mycelium (plural mycelia). The mycelium can be considered the main body or form of the fungus and is often described a s being filamentous. Growth occurs by the asexual reproduction of hypha, which grow into branching chains. Mycelium is important to the fungus because it can navigate through soil or wood and use that substrate as food, which the fungus will need if it is to produce fruit bodies (e.g., basidoiocarps) such as mushrooms, brackets, truffles, cups, or morels.
Mycelia excrete exoenzymes which can kill living tissue (necrotrophic) and then absorb that dead material (saprotrophic), simply absorbing material that was already dead (again, saprotrophic), or by feeding off of living tissue (biotrophic).
While it is believed that all of the phyla of the Fungi kingdom contain filamentous species, the Ascomycota and Zygomycota phyla, in particular have a large number of filamentous species. The members of these phyla make a large variety of products such as proteins, amino acids, oils, medicinals (e.g., penicillin), food (e.g., tempeh), food additives, food preservatives (e.g., citric acid), and industrial enzymes as well as being used in baking, and the production of chees, beer, and wine.
State of the art solid-substrate fermentation (SSF) suffers from a number of distinct disadvantages. For example, the final product, i.e. the produced biomass, is intimately mixed with the solid substrate which is fundamentally difficult to separate one from the other. Typically, SSF produces fungal biomass in low concentrations, has very low conversion rates and ultimately results in low yields. SSF requires specific water activities for effective fermentation. Delivering and maintaining the right amount of water activity is difficult and expensive to implement. Aerating SSF systems is also difficult to accomplish, further exacerbating conversion efficiencies and limiting system yields. Improper water activity as well as poor aeration pose limitations to mass and heat transfer, which result in overheating and deficiencies in oxygen supply. The resulting biomass is characterized as having randomly oriented filaments, which greatly limit utility in certain applications; i.e. food and/or animal feed.
Quorn™, a product comprised primarily of the biomass of Fusarium venenatum filamentous fungi offers a relatively nutritional mycoprotein. Quorn™ is produced by a state of the art submerged fermentation system, capable of producing large volumes in a batch based continuous process. Although commercially viable, the production methodology suffers from a number of distinct disadvantages. In order to meet commercial demands, Quorn™ uses bioreactors that cost between $35-40 million each. The Quorn™ system is run continuously in a single reactor until the fungal system matures beyond key metrics or is contaminated by another species. At this point, production comes to a standstill, the reactor and all associated plumbing is emptied and sterilized, a process that can take weeks to complete and introduces a number of serious issues for a supplier of commercial product. Such issues are, for example, (1) difficult to predict production cycles, (2) costs incurred for cleaning and stopping production, (3) difficulties in controlling inventory, etc. Further, submerged fermentation in large bioreactors requires tremendous amounts of energy to aerate and mix. Separation of the biomass from the liquid in which it ferments requires centrifugation, which is also known to be a capital intensive and energy demanding process. The process is further water intensive, necessitating the handling of large amounts of waste water. The biomass produced is characterized as having short filament lengths, which limits its ability to directly convert to food/feed products without introducing bind agents and subsequent process steps which incur further costs, difficulties and effort to effectively manage.
The present filamentous mycelia growth methodologies suffer from a number of disadvantages. For example, facilities having the proper aeration and equipment needed for fungal growth and subsequent separation of the fungal mycelia from the growth media (e.g., centrifuges) require significant capital expenses, especially for conducting fungal growth on an industrial scale. Not only do the current processes require substantial energy and water inputs, but they also result in the generation of a large waste stream.
Consequently, there is a need in the industry for a streamlined approach to filamentous mycelia filamentous fungi biomat formation.